This invention relates to an automatic climate control for a motor vehicle heating, ventilation and air-conditioning (HVAC) system, and more particularly to a control that enables separate calibration of the transient and steady-state control phases.
The operation of a vehicle automatic climate control can be characterized as including a transient phase and a steady-state phase. The transient phase ordinarily commences when the control is activated and the cabin temperature is uncomfortably warm or cool. In this situation, the control objective is to choose HVAC settings (such as blower speed and air discharge temperature) that will quickly take the cabin to a neutral reference temperature, such as 75xc2x0 F. The steady-state phase follows the transient phase, and adjusts the HVAC settings as required to maintain the cabin at the reference temperature (or some other desired temperature) as the ambient temperature or solar loading vary.
A common way of carrying out the above-described control is to estimate the required heating or cooling effort of the HVAC system based on ambient temperature, solar loading, and so on, and to schedule the blower speed and air discharge temperature in a pre-programmed fashion based on the required effort. An example of such a system is shown in FIGS. 1A and 1B, where an occupant set temperature Tset, and measures or estimates of ambient temperature Tamb, solar intensity Tsolar and cabin air temperature Tin-car are combined with a constant K to form a Program Number (PN) that represents the required effort of the HVAC system. As indicated in FIG. 1A, PN decreases in response to increasing values of Tamb, Tsolar and Tin-car to provide increased cooling, and increases in response to increasing values of Tset to provide increased heating. As indicated in FIG. 1B, the blower speed (BLS), the air discharge temperature (ADT) and the air inlet and discharge locations (MODE) are then scheduled as a function of PN. Typically, the HVAC settings and program number gains are calibrated for steady-state operationxe2x80x94that is, so that the reference temperature will be maintained under various ambient conditions. The same schedule of HVAC settings is used under transient conditions, where the value of Tin-car following an ambient-soak condition biases PN to a high or low initial value that evokes a strong heating or cooling response. For example, when the system is activated following a hot-soak period (after several hours in a parking lot on a hot sunny day, for example), Tin-car is relatively high; this produced a PN value that is relatively low, and the HVAC schedule calls for a high blower speed and low air discharge temperature. As the cabin temperature and Tin-car are reduced, PN increases, and the blower speed and air discharge temperatures follow the pre-programmed schedule. When Tin-car reaches the reference temperature (or Tset), the transient phase is considered to be concluded, and the system operates in the steady-state phase.
A drawback of the control approach described in the preceding paragraph is that the system response during the transient phase is defined by a schedule that is calibrated for the steady-state phase. Consequently, the transient response can only be changed by changing the steady state response; and conversely, changing the steady-state settings also changes the transient response. In other words, calibration engineer can optimize either the steady-state phase performance or the transient phase performance, but not both. Typically, the HVAC settings are calibrated to optimize the steady-state phase performance, and the transient phase performance remains sub-optimal. Accordingly, what is needed is an improved climate control methodology that does not suffer from this limitation.
The present invention is directed to an improved motor vehicle automatic climate control methodology in which HVAC commands for transient phase operation are developed independent of the HVAC commands calibrated for steady-state phase operation. At system activation, a transient phase indicator is initialized based on the cabin temperature and the set temperature, and thereafter is updated to reflect progress toward steady-state phase operation. The steady-state HVAC commands are based on ambient conditions and the set temperature, and the HVAC commands at system activation are based on the steady-state commands and offsets based on the initial in-car temperature. A transient modifier based on the transient phase indicator brings the initial HVAC commands into correspondence with the steady-state HVAC commands as the cabin temperature approaches the set temperature. In a preferred embodiment, the transient modifier is a power function of the transient phase indicator, and the HVAC commands are clamped at the initial values until the transient phase indicator reflects a predetermined amount of progress toward the steady-state phase.